Re: [PATCH] block: make sure big bio is splitted into at most 256 bvecs

[Kent Overstreet]

On Wed, Apr 06, 2016 at 10:37:05AM +0800, Ming Lei wrote:
> On Wed, Apr 6, 2016 at 10:34 AM, Kent Overstreet
> <kent.overstreet@xxxxxxxxx> wrote:
> > On Wed, Apr 06, 2016 at 10:30:22AM +0800, Ming Lei wrote:
> >> Now limit.max_segments is for limiting segments from hw view, one this
> >> segment may include lots of pages/bvecs.
> >>
> >> The current bio_clone() issue is that we can't clone from one bio which
> >> includes more than 256 bvecs, maybe all these 256 bvecs belong to
> >> one same hw segment.
> >
> > So the distinction is purely a post multipage bvec thing?
> 
> Even after multipage bvec is applied, the limit for max bvecs is still needed
> for some cases like bio bounce, in which bio_clone() need to
> clone single page bvec.

s/max bvecs/max pages/?

What I meant is that until we have multipage bvecs, unless I'm missing something
max_segments is exactly what we want. After multipage bvecs, things do get more
complicated I agree.